Field of the Invention
The present invention relates to a cooling water passage structure in an internal combustion engine, which is an engine mounted to a vehicle such as a motorcycle.
Description of the Related Art
Conventionally, in a vehicle such as a motorcycle, as disclosed in Patent Document 1, for example, the cooling water passage is disposed inside the cylinder block and the cylinder head of the engine, which is the internal combustion engine. The inlet for cooling water is disposed on the cylinder block side, and the outlet is disposed on the cylinder head side. With this cooling water passage structure of engine, cooling water cooled by the heat exchanger first flows through the cylinder block to cool the cylinder block, and then flows into the cylinder head to cool the cylinder head. Finally, the cooling water is recirculated to the heat exchanger to be cooled again. Patent Document 1: Japanese Laid-open Patent Publication No. 04-350348
However, to sufficiently cool the cylinder head with the conventional cooling water passage structure, a larger amount of cooling water needs to flow into the cylinder block first. This conversely results in a tendency of overcooling of the cylinder block side. Leaving the cylinder block as it is may cause a problem such as a deterioration of combustion efficiency.